Langer-Giedion syndrome is characterized by cone-shaped epiphyses in the hand, multiple cartilaginous exostoses, shortness of stature, and characteristic craniofacial abnormalities, and mental retardation. The clinical features of Langer-Giedion syndrome are essentially identical to those of trichorhinophalangeal syndrome type I except that the latter does not include multiple exostoses and rarely includes mental retardation. The exostoses found in LGS are essentially identical to those seen in hereditary multiple exostoses, an autosomal dominant disorder characterized by multiple, cartilage-capped exostoses (benign tumors) on the juxtaepiphyseal regions of enchondral bones. The long term goal of this research project is the complete characterization at the molecular level of the genes which are responsible for the phenotypes associated with the Langer-Giedion syndrome and the related syndromes hereditary multiple exostoses and trichorhinophalangeal syndrome type 1. This application encompasses the following three specific aims which are directed at our long term goal. First is to isolate and characterize the genes located in the LGS region including TRPSI and any genes that may be involved in normal mental function. Second, isolate and characterize the gene for EXT2 present on chromosome 11 and look for clues as to how its function is related to EXT1. Third, use the mouse as a model system to analyze the role of EXT1 in bone development and tumorigenesis. Characterize the temporal and spatial pattern of EXT1 expression in the mouse using both RNA blot and in situ hybridization techniques determine the role this gene plays in vivo by analyzing mice with a null mutation in the EXT1 gene. The genes involved in the pathology of Langer-Giedion syndrome are likely to be involved in the normal development of bone and connective tissues and of normal mental capabilities. Understanding the functions of these genes may give us insights into these important developmental processes as well as tumor suppression. Molecular analysis of the Langer-Giedion genes will be an essential step towards a detailed understanding of their functions.